A process for steam cracking chlorine-containing feedstock

ABSTRACT

A method of processing a plastic and a method of processing pyoil derived from a plastic. A numerical model for a correlation between chlorine content in one or more process streams of a steam cracking unit and a hydrocarbon to steam ratio in a feed stream of the steam cracking unit is constructed. A pyoil and naphtha blend is mixed with steam at a hydrocarbon to steam ratio obtain from the model to produce the feed stream for a steam cracking unit. The feed stream is processed in the steam cracking unit to produce olefins.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisional Patent Application No. 63/123,998, filed Dec. 10, 2020, which is hereby incorporated by reference in its entirety.

FIELD OF INVENTION

The present invention generally relates to steam cracking processes. More specifically, the present invention relates to a method of processing a plastic derived pyrolysis oil (“pyoil”) to produce a feed stream for a steam cracker.

BACKGROUND OF THE INVENTION

Chemical recycling of mixed plastic waste has become a new route for producing certified circular polymers. The recycling process includes pyrolysis of waste plastics, which yields a pyoil stream that typically contains a high level of contaminants including organic chlorine, organic nitrogen, and oxygenates. The presence of chlorine in the feedstock of a steam cracking unit leads to corrosion in radiant coils of the furnaces of the steam cracking unit. Additionally, in the downstream of the of olefins production plants, chlorine can lead to stress cracking corrosion.

Conventional methods of lowering chlorine contents in plastic derived pyoil include blending with naphtha and/or gas condensate. Naphtha or gas condensate usually contains 0.2-1.6 ppm of organic chlorides. Pyoil contains 67 ppm-521 ppm of organic chlorides. Thus, in order to reduce the effect of contaminants and render the pyoil safe for subsequent petrochemical units, the pyoil is blended with naphtha or gas condensate at a mass ratio of about 1:167 (pyoil:naphtha). However, using naphtha with a high naphtha to pyoil blending ratio is costly, resulting in high production cost for olefins and other valuable chemicals from pyoil.

Overall, while systems and methods for lowering chlorine level, in plastic derived pyoil exist, the need for improvements in this field persists in light of at least the aforementioned drawbacks for the conventional methods.

BRIEF SUMMARY OF THE INVENTION

A solution to at least the above mentioned problem associated with methods for lowering heteroatom contaminants content is discovered. The solution resides in a method for processing pyoil that includes mixing pyoil with naphtha and steam. This can be beneficial for diluting the contaminants in the pyoil without using a large amount of naphtha, thereby reducing production cost compared to conventional methods. Additionally, the disclosed method can further include constructing a numerical model for correlation between steam to hydrocarbon ratios and chlorine contents such that an optimized steam to hydrocarbon ratio can be determined to minimize the effect of the contaminants in a steam cracking unit while maintaining a low production cost for steam cracking the pyoil, compared to conventional methods. Therefore, the methods of the present invention provide a technical solution to the problem associated with the conventional methods for lowering contaminants in plastic derived pyoil.

Embodiments of the invention include a method of processing pyoil. The method comprises mixing a pyoil obtained via pyrolysis of plastics with naphtha to produce a hydrocarbon stream having a chlorine (element) content lower than a chlorine (element) content of the pyoil. The method includes mixing the hydrocarbon stream with steam to form a feed stream. The method includes steam cracking the feed stream under reaction conditions sufficient to produce olefins.

Embodiments of the invention include a method of processing pyoil. The method comprises mixing a pyoil obtained via pyrolysis of plastics with naphtha to produce a hydrocarbon stream comprising 1 to 3 ppm chlorine. The pyoil comprises more than 60 ppm chlorine. The method comprises mixing the hydrocarbon stream with steam at a steam to hydrocarbon mass ratio of greater than 0.35 to form a feed stream having a chlorine (element) content less than a chlorine content of the hydrocarbon stream. The method comprises steam cracking the feed stream under reaction conditions sufficient to produce olefins.

Embodiments of the invention include a method of processing plastics. The method comprises (a) processing plastics under pyrolysis conditions sufficient to produce a pyoil comprising hydrocarbons and more than 60 ppm chlorine. The method comprises (b) mixing the pyoil with naphtha to produce a hydrocarbon stream comprising 1 to 3 ppm chlorine. The method comprises (c) mixing the hydrocarbon stream with steam at a first steam to hydrocarbon ratio to produce a first feed stream. The method comprises (d) steam cracking, in a steam cracker, the feed stream under reaction conditions sufficient to produce an effluent stream comprising olefins, aromatics and steam. The method comprises (e) separating the effluent stream in a separation unit to produce one or more product streams comprising an ethylene stream, a propylene stream, a C₄ stream, and a pyrolysis gas stream. The method comprises (f) determining chlorine content of one or more process streams produced during steps (d) and (e). The method comprises (g) repeating steps (c) to (f) but with a second steam to hydrocarbon ratio in step (c) to obtain data for steam to hydrocarbon ratios and chlorine contents of the one or more process streams. The method comprises (h) constructing a numerical model for correlation between steam to hydrocarbon ratios and chlorine contents of the one or more process streams. The method comprises (i) determining a final steam to hydrocarbon ratio using the numerical model such that the chlorine contents for the one or more process streams are each below 3 ppm. The method comprises (j) operating the steam cracker using the final steam to hydrocarbon ratio to process the hydrocarbon stream.

The following includes definitions of various terms and phrases used throughout this specification.

The terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

The terms “wt. %”, “vol. %” or “mol. %” refer to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol. % of component.

The term “substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and/or the specification, include any measurable decrease or complete inhibition to achieve a desired result.

The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

The term “circular polymer,” as that term is used in the specification and/or claims, means a polymer made from ethylene or propylene, which is produced by steam cracking pyrolysis oil.

The term “chlorine content,” as the term is used in the specification and/or claims means concentration of chlorine element. The chlorine element exist in molecular structure(s) of chlorinated compound(s).

The use of the words “a” or “an” when used in conjunction with the term “comprising,” “including,” “containing,” or “having” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

The process of the present invention can “comprise,” “consist essentially of,” or “consist of” particular ingredients, components, compositions, etc., disclosed throughout the specification.

The term “primarily,” as that term is used in the specification and/or claims, means greater than any of 50 wt. %, 50 mol. %, and 50 vol. %. For example, “primarily” may include 50.1 wt. % to 100 wt. % and all values and ranges there between, 50.1 mol. % to 100 mol. % and all values and ranges there between, or 50.1 vol. % to 100 vol. % and all values and ranges there between.

Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic flowchart for a method of processing a plastic, according to embodiments of the invention;

FIG. 2 shows a schematic diagram of a cracking unit, according to embodiments of the invention;

FIG. 3 shows a schematic flowchart for a method of processing a pyoil, according to embodiments of the invention;

FIG. 4 shows comparison of measured chlorine levels with model predicted chlorine levels in process water of a steam cracking unit;

FIG. 5 shows comparison of measured chlorine levels with model predicted chlorine levels in a steam/liquid water separator bottom stream of a steam cracking unit; and

FIG. 6 shows predicted chlorine concentration in process water as a function of steam to oil (hydrocarbon) ratio.

DETAILED DESCRIPTION OF THE INVENTION

Currently, plastic derived pyoil, which contains a high level of heteroatom contaminants including chlorine, is processed by blending the pyoil with a large amount of naphtha at a pyoil to naphtha mass ratio up to 1:167. This can be costly due to the high cost of naphtha, resulting in low financial feasibility of the whole process. The present invention provides a solution to this problem. The solution is premised on a method of processing pyoil. The disclosed method of processing pyoil includes blending the pyoil with naphtha to form a hydrocarbon stream and further diluting the hydrocarbon stream with steam to produce a feed stream for steam crackers that has a chlorine level that is safe for the steam cracking units. This can significantly reduce the amount of naphtha needed for blending with pyoil, thereby reducing the overall cost for lowering chlorine level in pyoil. The disclosed method can include constructing a numerical model correlating hydrocarbon stream to steam mass ratio and chlorine contents of one or more process streams in a steam cracking unit. The numerical model can be used to obtained an optimized hydrocarbon to steam mass ratio that can ensure production efficiency and low chlorine level in the steam cracking unit, resulting in improved production efficiency from pyoil and increased safety level of processing pyoil. These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. Methods for Processing Plastics

In embodiments of the invention, the method for processing plastics comprises constructing a numerical model that correlates hydrocarbon to steam ratio with chlorine levels in process streams in steam cracking units. With reference to FIG. 1 , a flow chart is shown for method 100 of processing plastics.

According to embodiments of the invention, as shown in block 101, method 100 includes processing plastics under pyrolysis conditions sufficient to produce a pyoil comprising hydrocarbons and more than 60 ppm chlorine. In embodiments of invention, the plastics comprise polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. The pyrolysis conditions include a pyrolysis temperature of 300 to 700° C. and all ranges and values there between including ranges of 300 to 350° C., 350 to 400° C., 400 to 450° C., 450 to 500° C., 500 to 550° C., 550 to 600° C., 600 to 650° C., and 650 to 700° C. The pyrolysis conditions further include a pyrolysis pressure of 1 to 5 bar. In embodiments of the invention, the pyoil comprises 60 to 600 ppm chlorine and all ranges and values there between including ranges of 60 to 120 ppm, 120 to 180 ppm, 180 to 240 ppm, 240 to 300 ppm, 300 to 360 ppm, 360 to 420 ppm, 420 to 480 ppm, 480 to 540 ppm, and 540 to 600 ppm.

According to embodiments of the invention, as shown in block 102, method 100 includes mixing the pyoil with naphtha to produce a hydrocarbon stream. The hydrocarbon stream can comprise 1 to 3 ppm chlorine and all ranges and values there between including ranges of 0.1 to 0.3 ppm, 0.3 to 0.6 ppm, 0.6 to 0.9 ppm, 0.9 to 1.2 ppm, 1.2 to 1.5 ppm, 1.5 to 1.8 ppm, 1.8 to 2.1 ppm, 2.1 to 2.4 ppm, 2.4 to 2.7 ppm, and 2.7 to 3.0 ppm. In embodiments of the invention, the pyoil and the naphtha are mixed at a pyoil to naphtha mass ratio of 1:400 to 1:60 and all ranges and values there between. In embodiments of the invention, the naphtha includes light virgin naphtha, and/or full range naphtha. In embodiments of the invention, naphtha can include C₄ to C₁₀ hydrocarbons.

According to embodiments of the invention, as shown in block 103, method 100 includes mixing the hydrocarbon stream with steam at a first steam to hydrocarbon ratio to produce a first feed stream. In embodiments of the invention, the steam is at a temperature of 180 to 300° C. The first steam to hydrocarbon ratio can be in a range of 0.35 to 1.0 and all ranges and values there between including ranges of 0.35 to 0.40, 0.40 to 0.45, 0.45 to 0.50, to 0.55, 0.55 to 0.60, 0.60 to 0.65, 0.65 to 0.70, 0.70 to 0.75, 0.75 to 0.80, 0.80 to 0.85, to 0.90, 0.90 to 0.95, 0.90 to 0.95, and 0.95 to 1.0.

According to embodiments of the invention, as shown in block 104, method 200 includes steam-cracking, in a steam cracker, the first the feed stream under reaction conditions sufficient to produce an effluent stream comprising olefins, aromatics, and steam. In embodiments of the invention, at block 104, the reaction conditions can include a cracking temperature of 780 to 870° C. and a residence time of the steam cracker of 10 to 700 ms.

According to embodiments of the invention, as shown in block 105, method 100 includes separating the effluent stream in a separation unit to produce one or more product streams comprising an ethylene stream comprising primarily ethylene, a propylene stream comprising primarily propylene, a C₄ stream comprising primarily C₄ hydrocarbons, and a pyrolysis gas stream comprising pyrolysis gas.

In embodiments of the invention, the steam cracking at block 104 and separating at block 105 are implemented in steam cracking unit 200, as shown in FIG. 2 . Cracking unit 200 can include steam cracker 201 configured to receive feed stream 11 obtained at block 103 and crack feed stream 11 to produce effluent stream 12 comprising olefins, aromatics, and steam. Cracking unit 200 can include primarily fractionator 202 configured to separate effluent stream 12 to form first top stream 13 comprising olefins, aromatics, and steam, carbon black oil stream 14 comprising primarily carbon black oil, and cracked distillate stream 15 comprising primarily naphthalenes. Cracking unit 200 can further include water quench column 203 configured to quench first top stream 13 to produce quench water stream 16 comprising primarily water and 0.1 to 20 ppm chlorine, quench effluent stream 18 comprising primarily C₁ to C₅ hydrocarbons, and pygas stream 17 comprising C₅+ pyrolysis gasoline. In embodiments of the invention, an outlet of water quench column 203 is in fluid communication with an inlet of steam/liquid water separator 220 such that quench water stream 16 flows from water quench column 203 to steam/liquid water separator 220. Steam liquid water separator 220 can be configured to separate quench water stream 16 to produce (1) purge stream 42 comprising water and contaminants including chlorine, and (2) recycle stream 41 comprising steam. Recycle stream 41 can be flowed back to steam cracker 201.

Cracking unit 200 can include compressor 204 configured to compress quench effluent stream 18 to produced compressed effluent stream 19 and additional pygas stream 20. Additional pygas stream 20 can include a liquid fraction of quench effluent stream 18. In embodiments of the invention, pygas stream 17 and additional pygas stream 20 can form combined pygas stream 38. In embodiments of the invention, combined pygas stream 38 comprises 0.1 to 1 ppm chlorine element. According to embodiments of the invention, cracking unit 200 can include acid removal unit 205 configured to remove acid from compressed effluent stream 19 to produce acid stream 21 comprising one or more acids and acid-free effluent stream 22. Acid-free effluent stream 22 can be compressed in second compressor 206 and then cooled down in cold box 207 to form light stream 23 comprising primarily methane and hydrogen, collectively, and demethanizer feed stream 24. Cracking unit 200 can further comprise demethanizer 208 configured to remove methane from demethanizer feed stream 24 to form methane stream 25 and deethanizer feed stream 26. In embodiments of the invention, methane stream 25 is recycled back to cold box 207. Deethanizer feed stream 26 can be further processed in deethanizer 209 to produce C₂ stream 27 comprising primarily C₂ hydrocarbons and depropanizer feed stream 28. C₂ stream 27 may be further processed in acetylene extraction unit 210 to remove acetylene stream 29 comprising primarily acetylene, and then in C₂ splitter 211 to produce ethylene stream 30 comprising primarily ethylene, and ethane stream 31 comprising primarily ethane.

Cracking unit 200 can further comprise depropanizer 212 configured to separate depropanizer feed stream 28 to form C₃ stream 32 comprising primarily C₃ hydrocarbons, and debutanizer feed stream 33. C₃ stream 32 may be further processed in MAPD reactor 213 and C₃ splitter 214 to produce propylene stream 34 comprising primarily propylene, and propane stream 35 comprising propane. MAPD reactor 213 can be configured to remove methyl acetylene and propadiene (MAPD) prior to entering C₃ splitter. In embodiments of the invention, cracking unit 200 can further include debutanizer 215 configured to separate debutanizer feed stream 33 to produce C₄ stream 36 comprising C₄ hydrocarbons, and C₅+ stream 37 comprising primarily C₅+ hydrocarbons. In embodiments of the invention, combined pygas stream 38 can be combined with C₅+ stream 37 to form final pygas stream 39. In embodiments of the invention, each of demethanizer 208, deethanizer 209, C₂ splitter 211, depropanizer 212, C₃ splitter 214, and debutanizer 215 includes a distillation column.

According to embodiments of the invention, as shown in block 106, method 100 comprises determining chlorine content of one or more process streams produced at blocks 104 and 105. In embodiments of the invention, the process streams at block 106 can include cracked distillate stream 15, feed stream 11, quench water stream 16, acid stream 21, combined pygas stream 38, debutanizer feed stream 33, final pygas stream 39, or combinations thereof. In embodiments of the invention, the determining of chlorine content at block 106 is conducted by sampling of inlet and downstream of the plant according to Cl mass balance. In embodiments of the invention, about 80% of the chlorine intake is in the process water (quench water stream 16).

According to embodiments of the invention, as shown in block 107, method 100 comprises repeating blocks 103 to 106 but with a second steam to hydrocarbon ratio at block 103 to obtain data for steam to hydrocarbon ratios and chlorine contents of the one or more process streams in cracking unit 200. In embodiments of the invention, the steam to hydrocarbon ratios are controlled in a range of 0.35 to 1.0 and all ranges and values there between including ranges of 0.35 to 0.40, 0.40 to 0.45, 0.45 to 0.50, 0.50 to 0.55, 0.55 to 0.60, to 0.65, 0.65 to 0.70, 0.70 to 0.75, 0.75 to 0.80, 0.80 to 0.85, 0.85 to 0.90, 0.90 to 0.95, 0.90 to 0.95, and 0.95 to 1.0.

According to embodiments of the invention, as shown in block 108, method 100 comprises constructing a numerical model for correlation between steam to hydrocarbon ratios and chlorine contents of the one or more process streams. In embodiments of the invention, the numerical model is constructed using sampling of inlet and downstream of the plant according to mass balance of Cl. In embodiments of the invention, a conversion rate of 88% was obtained for Cl in feed stream to end up in the process water (quench water stream 16). In embodiments of the invention, the numerical model is configured to predict chlorine content in the one or more process streams of cracking unit 200 using steam to hydrocarbon ratios as inputs.

According to embodiments of the invention, as shown in block 109, method 100 comprises determining a final steam to hydrocarbon ratio using the numerical model constructed at block 108 such that the chlorine contents for the one or more process streams of cracking unit 200 are each below a pre-determined level. The pre-determined level is configured to minimize corrosion rate in cracking unit 200. The pre-determined level can be 3 ppm. In embodiments of the invention, the determining includes plug in a target chlorine level by using a calculated value of conversion rate for Cl (e.g., 88%) from feed stream 11 to the process water (quench water stream 16). In embodiments of the invention, the target chlorine level is obtained at block 108. According to embodiments of the invention, as shown in block 110, method 100 can include operating the steam cracker (steam cracker 201 of cracking unit 200) using the final steam to hydrocarbon ratio obtained in block 109 to process the hydrocarbon stream.

B. Methods for Processing Pyoil

As shown in FIG. 3 , embodiments of the invention include method 300 of processing pyoil. According to embodiments of the invention, as shown in block 301, method 300 includes mixing a pyoil obtained via pyrolysis of plastics with naphtha to produce a hydrocarbon stream having a chlorine (element) content lower than a chlorine (element) content of the pyoil. In embodiments of the invention, the plastics include polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.

The pyoil can comprise more than 60 ppm elemental chlorines. In embodiments of the invention, at block 301, naphtha and pyoil are mixed at a mass ratio of up to 167:1, preferably 50:1. In embodiment of the invention, the naphtha includes hydrocarbons having a boiling range of 35 to 200° C. The pyoil includes hydrocarbons having a boiling range of 35 to 390° C. The pyoil comprises more than 60 ppm chlorine element, preferably 60 to 600 ppm chlorine and all ranges and values there between including ranges of 60 to 120 ppm, 120 to 180 ppm, 180 to 240 ppm, 240 to 300 ppm, 300 to 360 ppm, 360 to 420 ppm, 420 to 480 ppm, 480 to 540 ppm, and 540 to 600 ppm. The hydrocarbon stream comprises 1 to 3 ppm of chlorine element and all ranges and values there between including ranges of 1 to 1.2 ppm, 1.2 to 1.4 ppm, 1.4 to 1.6 ppm, 1.6 to 1.8 ppm, 1.8 to 2.0 ppm, 2.0 to 2.2 ppm, 2.2 to 2.4 ppm, 2.4 to 2.6 ppm, 2.6 to 2.8 ppm, and 2.8 to 3 ppm.

According to embodiments of the invention, as shown in block 302, method 300 includes mixing the hydrocarbon stream with steam to form a feed stream. In embodiments of the invention, at block 302, the hydrocarbon stream is mixed with steam at a steam to hydrocarbon mass ratio of greater than 0.35, preferably 0.35 to 1 and all ranges and values there between including ranges of 0.35 to 0.40, 0.40 to 0.45, 0.45 to 0.50, 0.50 to 0.55, 0.55 to 0.60 to 0.65, 0.65 to 0.70, 0.70 to 0.75, 0.75 to 0.80, 0.80 to 0.85, 0.85 to 0.90, 0.90 to and 0.95 to 1. In embodiments of the invention, the feed stream comprises 0.2 to 1.6 ppm chlorine (element), preferably 0.2 to 0.8 ppm and all ranges and values there between including ranges of 0.2 to 0.3 ppm, 0.3 to 0.4 ppm, 0.4 to 0.5 ppm, 0.5 to 0.6 ppm, 0.6 to 0.7 ppm, and to 0.8 ppm. In embodiments of the invention, at block 302, the steam is at a temperature of 180 to 300° C. and all ranges and values there between including ranges of 180 to 190° C., 190 to 200° C., 200 to 210° C., 210 to 220° C., 220 to 230° C., 230 to 240° C., 240 to 250° C., 250 to 260° C., 260 to 270° C., 270 to 280° C., 280 to 290° C., and 290 to 300° C.

According to embodiments of the invention, as shown in block 303, method 300 includes steam cracking the feed stream under reaction conditions sufficient to produce olefins. In embodiments of the invention, the steam-cracking at block 303 is conducted in cracking unit 200. The olefins produced at block 303 include ethylene, propylene, C₄ olefins, or combinations thereof. Steam-cracking at block 303 can be conducted at a cracking temperature of 780 to 870° C. and all ranges and values there between including ranges of 780 to 790° C., 790 to 800° C., 800 to 810° C., 810 to 820° C., 820 to 830° C., 830 to 840° C., 840 to 850° C., 850 to 860° C., and 860 to 870° C. Steam-cracking at block 303 is conducted at a residence time in a range of 10 to 700 ms and all ranges and values there between including ranges of 10 to 50 ms, 50 to 100 ms, 100 to 150 ms, 150 to 200 ms, 200 to 250 ms, 250 to 300 ms, 300 to 350 ms, 350 to 400 ms, 400 to 450 ms, 450 to 500 ms, 500 to 550 ms, 550 to 600 ms, 600 to 650 ms, and 650 to 700 ms.

Although embodiments of the present invention have been described with reference to blocks of FIGS. 1 and 3 . It should be appreciated that operation of the present invention is not limited to the particular blocks and/or the particular order of the blocks illustrated in FIGS. 1 and 3 . Accordingly, embodiments of the invention may provide functionality as described herein using various blocks in a sequence different than that of FIGS. 1 and 3 .

The systems and processes described herein can also include various equipment that is not shown and is known to one of skill in the art of chemical processing. For example, some controllers, piping, computers, valves, pumps, heaters, thermocouples, pressure indicators, mixers, heat exchangers, and the like may not be shown.

As part of the disclosure of the present invention, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

Example Chlorine Contents of Process Water Streams in a Steam Cracking Unit

A pyoil comprising 50 to 226 ppm chlorine is blended with naphtha to reduce the chlorine concentration in the blend to 1 to 3 ppm. Regular steam cracker feedstocks such as gas condensate and naphtha contain chlorine at level of less than 0.1 to 1.0 ppm. Hence, by measuring of chlorine in the inlet, it is possible to calculate the plant's chlorine intake in kg/hr. Assuming that 88% of the chlorine intake ends up in process water (quench water stream 16 in FIG. 2 ), it is possible to predict chlorine concentration in process water downstream. The results are shown in FIG. 4 and FIG. 5 . As shown in FIGS. 4 and 5 , there is an acceptable agreement between chlorine concentration, which is measured in process water (quench water stream 16 in FIG. 2 ) by performing sampling and the predicted value (estimated based on the chlorine inlet).

FIG. 6 shows the predicted chlorine concentration in the process water as a function of steam-to-oil ratio. In creating this graph, it is assumed that all the furnaces process a feedstock with a maximum chlorine content of 3 ppm. With the same approach, it will be possible to determine maximum chlorine in the feedstock (naphtha/pyoil blend) to be processed on two furnaces and the remainder on the regular gas condensate.

In the context of the present invention, at least the following 12 embodiments are disclosed. Embodiment 1 is a method of processing pyoil. The method includes mixing a pyoil obtained via pyrolysis of plastics with naphtha to produce a hydrocarbon stream having a chlorine content lower than a chlorine content of the pyoil. The method further includes mixing the hydrocarbon stream with steam to form a feed stream. The method still further includes steam cracking the feed stream under reaction conditions sufficient to produce olefins. Embodiment 2 is the method of embodiment 1, wherein the pyoil contains more than 60 ppm chlorine. Embodiment 3 is the method of any of embodiments 1 and 2, wherein the hydrocarbon stream contains 1 to 3 ppm elemental chlorine. Embodiment 4 is the method of any of embodiments 1 to 3, wherein the feed stream has a chlorine content less than a chlorine content of the hydrocarbon stream. Embodiment 5 is the method of any of embodiments 1 to 4, wherein the hydrocarbon stream is mixed with steam at a mass ratio greater than 0.35. Embodiment 6 is the method of any of embodiments 1 to 5, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. Embodiment 7 is the method of any of embodiments 1 to 6, wherein the naphtha and the pyoil are mixed at a mass ratio of up to 167:1, preferably 50:1.

Embodiment 8 is a method of processing plastics. The method includes: (a) processing plastics under pyrolysis conditions sufficient to produce a pyoil containing hydrocarbons and more than 60 ppm chlorine; (b) mixing the pyoil with naphtha to produce a hydrocarbon stream containing 1 to 3 ppm chlorine; (c) mixing the hydrocarbon stream with steam at a first steam to hydrocarbon ratio to produce a first feed stream; (d) steam cracking, in a steam cracker, the first feed stream under reaction conditions sufficient to produce an effluent stream containing olefins, aromatics and steam; (e) separating the effluent stream in a separation unit to produce one or more product streams containing an ethylene stream, a propylene stream, a C₄ stream, and a pyrolysis gas stream; (f) determining chlorine content of one or more process streams produced during steps (d) and (e); (g) repeating steps (c) to (f) but with a second steam to hydrocarbon ratio in step (c) to obtain data for steam to hydrocarbon ratios and chlorine contents of the one or more process streams; (h) construct a numerical model for correlation between steam to hydrocarbon ratios and chlorine contents of the one or more process streams; (i) determining a final steam to hydrocarbon ratio using the numerical model such that the chlorine contents for the one or more process streams are each below 3 ppm; and (j) operating the steam cracker using the final steam to hydrocarbon ratio to process the hydrocarbon stream. Embodiment 9 is the method of embodiment 8, wherein the separating at step (e) can include separating effluent stream from the steam cracker to produce a top stream containing C₁-C₈ hydrocarbons and steam, a cracked distillate containing C₉-C₁₂ hydrocarbons, and carbon black oil containing C₁₂+ hydrocarbons. Embodiment 10 is the method of any of embodiment 8 and 9, wherein step (e) further includes quenching the top stream to produce a quench water stream containing 0.1 to 20 ppm chlorine, a quench effluent stream containing ethylene, propylene, C₄ hydrocarbons, C₅+ hydrocarbons, and a pygas stream containing C₅+ hydrocarbons. Embodiment 11 is the method of any of embodiments 8 to 9, wherein the pygas stream is combined with a compressed liquid fraction of the quench effluent stream to form a combined pyrolysis gas stream. Embodiment 12 is the method of any embodiments 8 to 10, wherein the combined pyrolysis gas stream contains 0.1 to 1 ppm chlorine. All embodiments described above and herein can be combined in any manner unless expressly excluded.

Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

1. A method of processing pyoil, the method comprising: mixing a pyoil obtained via pyrolysis of plastics with naphtha to produce a hydrocarbon stream having a chlorine content lower than a chlorine content of the pyoil; mixing the hydrocarbon stream with steam to form a feed stream; and steam cracking the feed stream under reaction conditions sufficient to produce olefins.
 2. The method of claim 1, wherein the pyoil comprises more than 60 ppm chlorine.
 3. The method of claim 1, wherein the hydrocarbon stream comprises 1 to 3 ppm elemental chlorine.
 4. The method of claim 1, wherein the feed stream has a chlorine content less than a chlorine content of the hydrocarbon stream.
 5. The method of claim 1, wherein the hydrocarbon stream is mixed with steam at a mass ratio greater than 0.35.
 6. The method of claim 1, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.
 7. The method of claim 1, wherein the naphtha and the pyoil are mixed at a mass ratio of up to 167:1, preferably 50:1.
 8. A method of processing plastics, the method comprising: (a) processing plastics under pyrolysis conditions sufficient to produce a pyoil comprising hydrocarbons and more than 60 ppm chlorine; (b) mixing the pyoil with naphtha to produce a hydrocarbon stream comprising 1 to 3 ppm chlorine; (c) mixing the hydrocarbon stream with steam at a first steam to hydrocarbon ratio to produce a first feed stream; (d) steam cracking, in a steam cracker, the first feed stream under reaction conditions sufficient to produce an effluent stream comprising olefins, aromatics and steam; (e) separating the effluent stream in a separation unit to produce one or more product streams comprising an ethylene stream, a propylene stream, a C₄ stream, and a pyrolysis gas stream; (f) determining chlorine content of one or more process streams produced during steps (d) and (e); (g) repeating steps (c) to (f) but with a second steam to hydrocarbon ratio in step (c) to obtain data for steam to hydrocarbon ratios and chlorine contents of the one or more process streams; (h) construct a numerical model for correlation between steam to hydrocarbon ratios and chlorine contents of the one or more process streams; (i) determining a final steam to hydrocarbon ratio using the numerical model such that the chlorine contents for the one or more process streams are each below 3 ppm; and (j) operating the steam cracker using the final steam to hydrocarbon ratio to process the hydrocarbon stream.
 9. The method of claim 8, wherein the separating at step (e) can include separating effluent stream from the steam cracker to produce a top stream comprising C₁-C₈ hydrocarbons and steam, a cracked distillate comprising C₉-C₁₂ hydrocarbons, and carbon black oil comprising C₁₂+ hydrocarbons.
 10. The method of claim 8, wherein step (e) further comprises: quenching the top stream to produce a quench water stream comprising 0.1 to 20 ppm chlorine, a quench effluent stream comprising ethylene, propylene, C₄ hydrocarbons, C₅+ hydrocarbons, and a pygas stream comprising C₅+ hydrocarbons.
 11. The method of claim 10, wherein the pygas stream is combined with a compressed liquid fraction of the quench effluent stream to form a combined pyrolysis gas stream.
 12. The method of claim 11, wherein the combined pyrolysis gas stream comprises 0.1 to 1 ppm chlorine.
 13. The method of claim 3, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.
 14. The method of claim 4, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.
 15. The method of claim 5, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.
 16. The method of claim 7, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.
 17. The method of claim 8, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.
 18. The method of claim 9, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.
 19. The method of claim 10, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof.
 20. The method of claim 11, wherein the plastic includes polyolefins, polyethylene terephthalate (PET), polyamide (PA) and polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), or combinations thereof. 